1. Field of the Invention
The present invention relates to a method and an apparatus enabling two dissimilar metal sheets with different physical properties to be bonded together by liquid phase diffusion bonding. Specifically, the present invention relates to a liquid phase diffusion bonding technique enabled to ensure sufficient bonding strength for a short period of time without using inert gas.
2. Description of the Related Art
It is widely known that, where dissimilar metal materials such as iron and aluminum are welded together, an intermetallic compound is generated at the bonding interface, resulting in insufficient bonding strength.
An example of means for boding such dissimilar metal materials is a liquid phase diffusion bonding method which ensures predetermined bonding strength. (See Joining of An Iron Pipe to An Aluminum Pipe by Zinc Plating, Quarterly Journal of the Japan Welding Society, Vol. 18, No. 4, pp. 572–579, 2000.)
The method described in the above document is as follows: an iron pipe with a tapered end is electro-plated with zinc; the iron pipe is inserted into an aluminum pipe and heated to predetermined temperature; and the iron pipe is further pushed into the aluminum pipe so that the pipes are bonded together by liquid phase diffusion.
This liquid phase diffusion bonding has the following mechanism. First, the iron pipe and the aluminum pipe are heated up over 381° C. (the eutectic temperature of zinc and aluminum), and the iron pipe is inserted into the aluminum pipe. When the iron pipe is inserted into the aluminum pipe, the end of the aluminum pipe is rubbed against the iron pipe so the new surfaces of both pipes come into contact with each other, thus aluminum and zinc react forming an eutectic liquid. This eutectic liquid accelerates a diffusion reaction of aluminum, zinc and iron, so that the pipes are bonded.
Another example of means for bonding dissimilar metal materials is to press two or more heated dissimilar metal sheets by using a pressure roller to bond them together. This bonding method is employed in manufacturing cladding material.